This invention relates to a throttle valve control system for an engine which detects the amount of movement of the accelerator pedal with an accelerator position sensor to electronically control the throttle valve.
In a conventional throttle valve control system, for instance, in a motor vehicle, the accelerator pedal is coupled through a mechanical link to the throttle valve as shown in FIG. 5.
FIG. 5 outlines the arrangement of the conventional throttle valve control system which is adapted to mechanically drive the throttle valve. In FIG. 5, reference numeral 1 designates an air intake passageway of an engine (not shown); 2, a throttle valve arranged in the air intake passageway 1; and 3, an accelerator pedal which is operated to manually open and close the throttle valve 2. The accelerator pedal is coupled to the throttle valve 2 through an intermediate link 6 consisting of an accelerator wire 4 and a pulley 5.
The intermediate link 6 is so designed that the degree of opening of the throttle valve changes non-linearly with the amount of action of the accelerator pedal 3 as shown in FIG. 6. FIG. 6 is a graphical representation indicating the relationship between the degree of opening of the throttle valve and the amount of action of the accelerator pedal.
The reason why the degree of opening of the throttle valve is changed non-linearly (in a sense of a quadratic curve) is that, when the accelerator pedal is positioned in a range from the position where it is not actuated to the position where it is halfway actuated (hereinafter referred to as "a low action range", when applicable), the accelerator pedal can be delicately operated to finely adjust the engine output and the vehicle speed. This feature is effective in the case where a motor vehicle is traveling on a congested road or in town; that is, in the case where it is necessary for the vehicle to move at a very low speed or to start and stop repeatedly. The delicate action of the accelerator pedal together with suitable braking operation makes it possible to adjust the vehicle speed with ease. On the other hand, when the accelerator pedal is positioned in a range of full action, an increment in the degree of opening of the throttle valve is larger than that in the amount of action of the accelerator. This is because when the engine should be accelerated greatly as in the case where the vehicle goes onto a highway, generally it is unnecessary to delicately control the engine output.
In the conventional throttle valve control system, as was described above, the intermediate link 4 is mechanically designed with the wire 4 and the pulley 5 so that the degree-of-opening characteristic of the throttle valve 2 is non-linear as shown in FIG. 6. Therefore, the throttle valve control system is limited in the degree of freedom in determining the degree-of-opening characteristic. For instance, it is difficult to obtain a degree-of-opening characteristic as indicated by the broken line in FIG. 6. Even if it is obtained, another problem is raised because it cannot be obtained without making the intermediate link 4 an intricate part of the structure. Furthermore, if the intermediate link 4 is determined to provide a certain degree-of-opening characteristic, then it is difficult to adjust the characteristic in conformance with the vehicle characteristic (such as the engine performance). In addition, the use of the wire 4 creates a problem in that hysteresis or operating delay occurs.
In order to eliminate the above-described difficulties, the use of the intermediate link has recently been suspended. A conventional throttle valve control system of this type is as shown in FIG. 7.
FIG. 7 is a block diagram outlining the arrangement of the conventional throttle valve control system. The device comprises an accelerator pedal position sensor 7 (hereinafter referred to merely as "an APS 7", when applicable) for detecting the amount of action of an accelerator pedal (not shown); a throttle valve actuator 8 coupled to a throttle valve (not shown); a throttle valve position sensor 9 (hereinafter referred to merely as "a TPS 9", when applicable); and a throttle valve controlling electric control unit 10 (hereinafter referred to as "a throttle valve controlling ECU 10", when applicable) for controlling the throttle valve actuator 8.
The APS 7 is so designed as to output a voltage in proportion to the amount of action of the accelerator pedal, and its output characteristic is as shown in FIG. 8.
The operation of the throttle valve controlling ECU 10 will now be described. The throttle valve controlling ECU 10 obtains an aimed degree-of-opening of the throttle valve referring to the amount of action of the accelerator pedal detected by the APS 7 and the throttle valve degree-of-opening map (the characteristic indicated by the broken line) as shown in FIG. 6, and performs feedback control so that the actual degree-of-opening of the throttle valve becomes the aforementioned aimed degree-of-opening of the throttle valve.
With the conventional throttle valve control system constructed as described above, the throttle valve degree-of-opening characteristic can be freely set by changing the throttle valve degree-of-opening map, and it can be adjusted according to the vehicle performance.
However, even if the throttle valve is electronically controlled to make the throttle valve degree-of-opening characteristic non-linear as was described above, the engine is not always high in operability when the accelerator pedal is positioned in the above-described low action range. This is due to the fact that detecting resolution of the APS 7 for detecting the degree-of-opening of the throttle valve is low.
In order to delicately operate the accelerator pedal to finely adjust the engine output and the vehicle speed, it is desirable that, even if the amount of movement of the accelerator pedal is small, the throttle valve is opened or closed with high responsibility. However, since the conventional APS 7 is low in detecting resolution during the low action range, the accelerator pedal must be operated greatly to some extent.
This problem can be solved by employing an APS which is high in detecting resolution. However, employing an APS which is high in detecting resolution raises another problem. That is, in the case where the accelerator pedal is positioned in the range of full action, it is unnecessary to have a high detecting resolution, and therefore half of the detecting region of the APS 7 is useless.
Furthermore, with the system, the degree-of-opening of the throttle valve is determined according to the amount of action of the accelerator pedal detected by the APS 7. Hence, if the APS 7 is out of order, the system cannot control the throttle valve any longer, so that the degree-of-opening of the throttle valve is fixed, and at worst the throttle valve may be fixed fully opened. Thus, the conventional device is not reliable in safety.